In the United States, approximately 15 million women experience hot flushes following the withdrawal of gonadal hormones during menopause. Hot flushes are characterized by an intense sensation of heat and the activation of heat loss mechanisms. For many individuals, hot flushes impair quality of life through physical discomfort, social stress, anxiety, and impaired sleep. Unfortunately, an effective, universally recommended treatment is not available. A prevalent view is that hot flushes occur in response to estrogen withdrawal from the central nervous system but little is known about this circuitry. The long-term objective of this application is to delineate circuitry underlying hot flushes and estrogen effects on thermoregulation. We hypothesize that estrogen effects on thermoregulation occur via neurons in the arcuate nucleus of the hypothalamus that contain NKB. In humans and other mammals, these neurons respond to ovarian hormone withdrawal with dramatic hypertrophy and increased expression of neurokinin B (NKB). Pilot studies in our laboratory have demonstrated that arcuate NKB neurons project to hypothalamic thermoregulatory nuclei and that central injection of agonists for the predominant NKB receptor (Neurokinin 3 receptor, NK3 receptor) can activate heat loss mechanisms. SPECIFIC AIM 1: Examine how neuronal network responses to temperature are altered by estrogen withdrawal, using Fos protein expression as a marker for neuronal activation. WORKING HYPOTHESIS 1: Estrogen withdrawal will lead to increased Fos expression in response to ambient temperatures at which low-estrogen animals exhibit greater activation of heat loss mechanisms. Specifically, increased Fos expression will be observed in neurons in the MnPO that express NK3 receptor as well as neurons in thermoregulatory nuclei of the hypothalamus and brainstem. SPECIFIC AIM 2: Investigate if pharmacological activation of NK3 receptors in the median preoptic nucleus will increase the activation of heat loss mechanisms and neurons in thermoregulatory brain areas. WORKING HYPOTHESIS 2: Microinjection into the MnPO of an agonist for the NK3 receptor will activate heat loss effectors (eg. cutaneous vasodilatation and behavior) and increase Fos expression in thermoregulatory nuclei associated with the activation of heat loss mechanisms. We expect these experiments to identify neuronal circuitry underlying estrogen modulation of thermoregulation. This knowledge should prove highly relevant for the design of improved treatments for hot flushes, a neurological phenomenon that reduces the quality of life for millions of aging women.